1. Field of the Invention
The invention relates to a process for checking the ability to function of a burner being disposed in an exhaust pipe of an internal combustion engine and being operated with a fuel/air mixture for heating up an exhaust-gas catalytic converter of the internal combustion engine, including a first and a second lambda probe being respectively disposed upstream and downstream of the exhaust-gas catalytic converter, each emitting an output signal corresponding to a respective residual oxygen content in exhaust gas and having signal levels representing either a rich or lean mixture composition.
Pollutant emissions from an internal combustion engine can be reduced in an effective manner by catalytic aftertreatment with a three-way catalytic converter in conjunction with a lambda closed-loop control device. However, an important prerequisite therefor is that both the lambda probe of the closed-loop control device and the catalytic converter have reached their operating temperature. Various heating measures have already been proposed for raising those two components of the exhaust emission control system rapidly to their operating temperature.
While heating the lambda probe, which has a low mass in relation to the catalytic converter, through the use of an electric heating device, presents no technical problems whatsoever, providing the electrical energy from the electrical system of a motor vehicle for rapid heating up of the catalytic converter in many cases exceeds the capacity of the electrical system of the vehicle.
In order to nevertheless reduce pollutant emissions during the cold-starting phase of the internal combustion engine, in which about 70 to 80% of the total HC and CO pollutants are emitted, it is known from German Published, Non-Prosecuted Patent Application DE 41 32 814 A1 to install an additional burner, fed with internal combustion engine fuel, in the exhaust line upstream of the catalytic converter and to thereby heat the catalytic converter rapidly to its operating temperature of about 300.degree. C. (Light-off Temperature). In order to achieve as short a heat-up time as possible, the burner is disposed directly in front of the catalytic converter. The fuel is fed to the burner from a fuel rail in a fuel circuit of the internal combustion engine, and air required for combustion is supplied by a secondary air blower which nowadays is often standard. In conventional practice, such a secondary air blower is used to blow air into the exhaust line of the internal combustion engine near exhaust valves in order to achieve preoxidization of exhaust gases.
Since such a burner is thus part of the overall exhaust system of the internal combustion engine, and the burner also produces its own emissions, the burner must be monitored in terms of its ability to function regarding limiting values to be complied with for pollutant emissions.
On one hand, the burner-specific emissions are influenced not only by the integrity of the burner ignition but also by the air ratio of the burner, and on the other hand, the burner air ratio influences the heating-up behavior of the catalytic converter. The air ratio of the burner is thus relevant to the exhaust gas and must be monitored by suitable measures.